1. Field of the Invention
The present invention relates to a grommet, and more particularly to the grommet including a corniced part and engaging parts, and formed in such a manner that the corniced part is smaller in diameter than the engaging parts. The invention also relates to a method of producing the grommet.
2. Description of the Related Art
Recently, so called power window systems have been installed on vehicle doors so that window panels can be easily opened and closed up and down by operating an electric motor provided therefor. The vehicle doors are also provided with speakers, door locks, and so on. Therefore, the electric motor for the power window system and so on must be supplied with power, and wire harnesses are equipped across chassis and the doors.
Usually, each of the wire harnesses is protected by an elastically deformable grommet from water and dust. The grommet includes a corniced part and two engaging parts. The corniced part is formed to have a smaller diameter than the engaging parts which are integrally formed on opposite ends of the corniced part. The engaging parts are adapted to be engaged with a chassis panel and a door panel respectively.
The conventional grommet has been made of rubber which is heavy (its specific gravity is about 1.3), and has badly affected weight reduction of an automobile. Moreover, rubber must be subjected to vulcanizing process which requires lot of working time, and productivity of the grommet has been poor. Further, because rubber is unable to be recycled, effective use of resources has been impossible.
The present invention has been made in view of the above described problems, and it is an object of the invention to provide a grommet which is light weight, able to be recycled, and excellent in productivity, and also a method of producing the grommet.
In order to solve the above described problems, according to one aspect of the present invention, there is provided a grommet comprising a corniced part in a shape of a bellows, and two engaging parts integrally formed on opposite ends of the corniced part and adapted to be engaged with respective bodies to be fitted, the grommet being formed in a hollow tubular shape in such a manner that the corniced part is smaller in diameter than the engaging parts, wherein the grommet is molded of thermoplastic elastomer by injection molding, and a diameter of the engaging parts is set to be less than five times as large as the diameter of the corniced part.
According to another aspect of the present invention, there is proposed a method of producing a grommet including a corniced part in a shape of a bellows, and two engaging parts integrally formed on opposite ends of the corniced part and adapted to be engaged with respective bodies to be fitted, the grommet being formed in a hollow tubular shape in such a manner that the corniced part is smaller in diameter than the engaging parts, comprising steps of molding thermoplastic elastomer into the grommet by injection molding so that the diameter of the engaging parts is less than five times as large as the diameter of the corniced part, opening molds for forming an outer face thereof, and thereafter, enlarging the corniced part in diameter, thereby removing the grommet from a core for forming an inner face thereof.
According to the first aspect of the present invention, because material for the grommet is thermoplastic elastomer, it is light weight and can be recycled. Moreover, the vulcanizing process will not be required. Meanwhile, since the engaging parts have the diameter which is less than five times as large as the diameter of the corniced part, the grommet can be produced by injection molding. Accordingly, after the molding, the core portion for forming the engaging parts can be passed through the corniced part without difficulty. This will make the molding time shorter, and stabilize dimensional accuracy of an inner face of the grommet.
According to the second aspect of the present invention, there is employed the method of producing the grommet by injection molding of thermoplastic elastomer. Because the thermoplastic elastomer which is similar to rubber in characteristics is employed as material, the grommet thus obtained is light weight. Further, it has become possible not only to recycle the material but to produce the grommet by employing injection molding, resulting in a rapid molding. Still further, dimensional accuracy of the inner face of the grommet will be stabilized, and, of course, vulcanizing process is not required. By molding the grommet by injection molding in such a manner that a ratio in diameter between the engaging parts and the corniced part is less than five, the core portion for forming the engaging parts can be passed through the corniced part without difficulty, after the molding.